Passive Biamping: How much improvement?

Jigesh,

About a year ago, I bought a used Carver AV-705x, 5 channel amp off of e-bay. At that time, I was using a Pioneer Elite VSX-09TX Flagship receiver. My intentions were to bi-amp my front Paradigm Monitor 7's with (4) of the channels, and run the CC-350 center channel with the 5th channel. I used the VSX-09TX for my rear speakers. But shortly after I got the Carver hooked up, one of the amp channels stopped working, so I ran the center with my receiver. The addition of the amp made the fronts really sound great!!

About a month and a half ago, my receiver was damaged in an electrical storm. I decided at that time to purchase an Outlaw 950 pre/pro, since my receiver was older and didn't have 5.1 inputs to mate up with my Pioneer Elite DV-47Ai DVD, SACD, DVD-A player. While I was waiting delivery of my new pre/pro, I had the Carver fixed. (blown fuse...$17.50)

I am now running all (5) channels with the Outlaw and Carver combo, hence I can no longer bi-amp my mains. I have actually heard an improvement in sound quality. Is it the Outlaw??? Was bi-amping really contributing anything??? IMHO, passive bi-amping doesn't benefit the sound of a speaker!!! Hope this helps!!!

When you say passive biamping, you know that this can only be accomplished by completely getting rid of the internal speaker crossovers from the amp to speaker path? Biamping uses an external crossover to send one section of the whole signal to each driver. The only difference between passive and active biamping is the type of crossover used to split the signal BEFORE it reaches the amplifier. Once the signals are split, each piece of the signal goes to a single amplifier channel, which then feeds the signal directly to the driver unit. If you are unable to seperate the drivers from the internal speaker crossover, then you cannot biamp. Just using a single amp channel to send a signal to each set of binding posts is called Fool's Biamping, since you are still using the speaker's internal crossover.

As for the improvement in your system, there will probably be a slight improvement, but it will probably not be worth the price of another set of amp channels. As always with audio, the law of diminishing returns takes place when biamping (JMHO, though).

Why not try it with four channels from the amp now and see if you hear a difference in 2 channel? I'm bi amping my mains and it was quite a noticeable improvement in sound stage depth but then my mains are fairly demanding for power.

i don't think removing the strap results in the drivers being electrically isolated from each other. you could always dash off an email to Paradigm to confirm.

By just removing the jumper you are not bypassing the internal crossovers. You will only be separating the modes of power delivery for the drivers. The whole idea of biamping is to have one amp channel use its power to deliver one section of the full spectrum of sound. By using the internal crossovers of the speaker, each amp channel is still delivering a full ranges signal through each set of speaker wire, a signal which only separates by the time it reaches the crossover network of the speaker. To completely bypass the crossover, you would have to take the jumpers off, then disconnect the drivers and binding posts from the crossover and connect the binding posts to the drivers directly.

While chung is adament that you must bypass the internal x-over to properly biamp, increasing headroom can greatly improve dynamics and of course help with overall output.

Biamping with seperate passive x-overs is a completely idiot suggestion...

Uh, the strap simply connects the woofer and tweeter sections in parallel. Just as there is nothing wrong with removing the strap to bi-wire, there is nothing wrong with removing the strap and connecting separate amplifiers to the two posts. You might not find much of an improvement, though.

Why else are they there then?

BTW "Fool's biamping" with wholly separate amps might give some improvement in sound if the power supply of the amps being used are struggling with the power requirements (ie rail voltages sagging) when used alone. In this case, just running each speaker singly from a power amp should achieve the same result. "Fool's biamping" with multiple channels from a single multichannel amp will only have an effect if each amp section has its own separate power supply (which is usually not the case).

Thats absolutely incorrect craig....

why Tyler?

Baucause, unless I'm misreading, you are suggesting that all multiple channel amps without mulitple seperate ps's will not make more power with 4 channels driven as opposed to 2 channels. This simply isn't the case...

In the vast majority of cases, they're there because the public, or some portion thereof, demands it and not for any positive benefit. No sense in alienating potential customers as it's cheap to implement. Those that want that feature and enjoy the techo-speak are happy. Those that don't, it's irrelevent. Like including a cigarette lighter in a car. If there's a benefit, I think it has more to do with being able to provide additional power to a speaker that can use it.

FYI Guys..

A real Bi Amp Passive Internal Crossover has completely
isolated networks for High Band and Low Band(Or if the
Internal XO Network is TriAmpable it will have completely
seperated High Band, Mid Band and Low Band.

Removing the Shorting staps breaks the crossover down into
these seperated sections and thus using 2 channels of amp
per speaker (In Bi Amp Configuration) sends more power to
one particular section of the network.

To say this is not true Bi Amping is ridiculous IMHO. This
method of seperating the XO Regions allows you loads of
flexibility to do things like mingle Tube gear and S.S gear
or add more power to one particular section, or just add
more power on all sections of the XO.

There are immense benefits to be gained here!

As far as "Active Biamping" where the drivers are singly
connected directly to the amplifier and between the source
and amps resides an active external crossover. This would
only be adviseable if the speakers were designed from the
start to be used in such a setup.

To take a prebuilt set of speakers and eliminate the stock
Passive Networks entirely and rely on Active Externals like
Marchand or DBX Driveracks, should only be done by experts.
You have absolutely no clue how the designers did the stock
XO's and with Active's all you can do is adjust the Slope
and the Frequency. You have no way to configure them for
Baffel Step Compensation, Time Alignment etc.

If the speakers wern't designed and provided with external
active's then I think it's a bad idea to try and impliment
them with existing speakers.

Removing the plates should seperate the internal cross overs from each other allowing you to use two amp channels. This should improve the dynmaics of the speaker since you're now sending more power to each driver and unless the multichannel amp is very poorly designed it will be able to send more power then just using two channels. Ideally yes moving the crossovers before the amps would lower the work load on the amps since they'd only amp the freq's required but that's not to say there isn't any point in trying passive bi amping. Besides since he has a multichannel amp already just try it and see if its worth it to you...the proof's in the pudding as they say.

While this has been used as an alternative definition of "passive biamping," I read a series of articles (I dont remember where, but please don't flame me) that looked at the benefits of baimping in this way, and when those benefits were minimal at best, this method of biamping was decried as "fool's biamping." However, my reasons for calling this type of biamplification not valid are as such:

The whole idea of using the speaker's internal crossover is totally against the reason for biamplification. Biamplification's main benefit is to limit the amount of bandwidth frequency each amp channel delivers to the speaker, in effect decreasing the amount and extent of work each channel does, and in the end decreasing the chance of distorsion, clipping, and other harmful side-effects that occur when an amp is worked too hard while at the same time increasing headroom and clarity for the rnage of frequency that the amp delivers. However, when using the speaker's internal crossover, a full-range signal is still being sent to each set of binding posts. The internal crossover is sifting out the unneeded range of frequency, but the FULL RANGE SIGNAL is still being pushed out by each amp channel. Also, by using amp power to push out the full range signal, power is wasted because of the use of the internal crossover, which gets rid of the extra signal by soaking in the amp power that was used to generate it.

This method of biamping is essentially the same as biwiring with a more powerful amp, as opposed to using seperate amp channels to drive each frequency range. The benefits of "fool's biamping" are essentially the same as using biwire speaker cable and an amp with twice the power of the existing amp.

Here is an article you may find interesting:

http://www.sound.westhost.com/bi-amp.htm

Chung,

So wrong you are.. But hey that's fine...


I will stick with my "Fools" Bi Amplification rather than
some jerry rigged setup with an active crossover that does
not even take into account baffle step, time alignment or
numerous other "specific" crossover issues that go into
designing a proper network, passive or otherwise.

As a side note... Even IF the amp is sending a full range
signal to the crossover and then to the specific driver.
The amp is NOT under the same loads. As soon as you remove
those shorting straps on a properly designed crossover
network you are now driving "seperately" the tweeter and
midranges and the woofers. A woofer always will present a
lower impedance than a tweeter and will require more work
from the amplifier than the tweeter will. So it's not
accurate at all to say that "even though" the XO is now
seperated that the amps are still working just as hard
because it has to send a full range signal to the crossover.

*Shakes head* Keep reading... But perhaps you should "try"
it.. It's NOTHING at all like Bi Wiring, not even close.

Well I certainly wouldn't rip out the crossovers and try an active approach especially if the speakers were designed by competent engineers. I think Paradigm is competent

However, in this case, I'm assuming the poster wants to remove the strap and basically run two amps into the upper and lower binding posts. This, I assume, will be done without the amps having been preceded by any sort of active crossover (filter). If so, then both amps will certainly be presented with the same full range frequencies and they will do what amplifiers do: amplify the full range of frequencies. Hence any increase in the amp headroom would be very speculative. Were it that they were preceded by filters, then yes, I could see there being this headroom increase. The amp just doesn't know how the frequencies that it's sending out are being used. So I must politely disagree with you Brett.

Often what occurs, is a situation where the gains of the two amp are not critically matched. In this case you've changed the frequency response of the system. Run a little more juice up top and I'll just bet things might be called sparkling and greater delineation of cymbals and such. If you like it, who am I to argue with it? Since you own the equipment already, it's not going to hurt matters for you to play around.

However, if you carefully match, you may find that the primary benefit was to the person who sold you the amps.

On a side note, keep in mind that most of your acoustic power is down below. Only about 10% or so exists above ~ 3.5 kHz.

Brett, I know that an active crossover does none of these things, but at which point did I say that active biamping would take all these factors into account? Many times, especially with well designed speakers (Paradigm, B&W, Revel, Dynaudio) the internal crossover is far more favorable than an external crossover, as it has had months (maybe even years) or R&D put into its design and its implementation with the specific drivers that it is paired up with.



Again, when did I say that the amp is under the same loads? I hate it when people put words into my mouth. I said repeatedly that the loads on each amp channel in a "fool's biamped" situation will be more than an amp on a passive or active biamp setup. I NEVER said that the loads of a "fool's biamped" system would be the same as when the amp was powering both drivers. However, the amp channels are working harder in the "fool's" setup than the active or passive setup because they are always going to be pushing a full range signal which will have to be sifted through at some point(the internal crossover), instead of just pushing a constant signal along the path.

Now when you say that the drivers are "separated" from each other when you remove the shorting strap from the crossover, you do know that the drivers themselves are still connected to some sort of crossover, right? So while you are driving the tweeter, midrange and woofer "seperately," they are still connected to some sort of crossover inside the speaker. The path is not a clear path from amp to speaker wire to binding posts to driver, like in passive and active biamping.

As for Brett,
I think that you have posted rebuttals to statements that I NEVER made, statements that you guessed I would have said but nonetheless I NEVER wrote (or even thought, for that matter). This is a very bad habit in the HTF and in life, so it might be best to only post replies to statements and phrases instead of conjecture and assumption.

Now, on a personal note, I have tried active, passive, and fool's biamping as well as biwiring on a myriad of speakers (B&W, AAD, Revel, KEF, Paradigm) using a myriad of amps (McIntosh, Krell, Adcom, Rotel, B&K, Anthem, Odyssey), and for the most part have found that with enough power, and a good set of speaker wire and jumpers, just using a single two-channel amp provided the best sound for my tastes. More often than not, I found that in the fool's biamp setup, the most noticeable improvment in sound was more to do with the amount of total power as opposed to the removal of the shorting strap or jumper and the use of another amp.

As always, I will try to urge anyone to try it first, but it helps to exactly why one would try something new. The whole idea of Biamping is to help the amps as much as possible so that they can pass along the best possible signal to the speaker. However, simply passing along the signal doesnt take into account baffle alignment, driver deising, crossover points, phase shifts, or any other speaker-related issues any more than it takes into acount room treatment, listening position, or frequency holes. I believe that it just helps to know specifically WHY something should be done before actually doing it for experiment's sake.

Passive bi-amping improves sound mainly by reducing the current demands on the high frequency amplifier. However, active bi-amping will improve sound even more because the amplifier only amplifies the intended signal and nothing else (that would be filtered by a passive crossover), so the intermodulation distortion and any voltage swing related compression will be reduced. But it's important that the active crossover keep the same frequency response as the passive one... which can be difficult.

difficult? perhaps next to impossible considering the monumental task of 1st matching what the engineers made then 2nd improving upon it. IMHO, it you want to actively biamp, buy it that way.
so Jigesh, whatcha gonna do?

There seems to be quite a bit of mis-information here, so I'll try and help clear some things up.

In a passive bi-amp setup, where one is using the internal (passive) crossovers on a speaker with the various sections separated (ie any plates removed) then one has one amp powering the lowpass xover inputs, and one powering the highpass xover inputs.

The LOAD on each of these amps is LESS than the load present if one of the amps was driving both xover inputs in parallel (As is the case in a normal single amp situation.)

WHY?

Because the impedance of the tweeter+highpass network is high at low frequencys - there is a capacitor in series (and perhaps an inductor in parallel) with basically a resistive device (The driver) in the below 1kHz range. This presents a very high impedance which is very easy to drive - the current involved is minimal. Thus the amp is under less stress. It has higher current reserves for the highs (Which it doesn't need much for anyway as Chu indicates above).

What about the lows?

The impedance of the woofer plus any series inductors and parallelled caps rises at frequencies above the xover point. Thus, the load the amp must supply current to is reduced. Note that it is not reduced all that much as the power content of high frequencies is very low. Thus, one does not see the same advantages as for the tweeter amp.

What's the benefit of active biamping (possibly using a passive xover before the amps)?

This has the further effect in that the amp is no longer amplifying any signals outside of the small(ish) passband that the particular driver it is supplying is operating over. Thus one achieves all the benefits of the above PLUS the added benefit that there is no xover network between the amp and the speaker. This means that ALL the power that the amp is producing is used to drive the speaker. None get's wasted away through heat via the inductors and resistors etc. in the xover network. One sees benefits here for the amp supplying the lows as there is no series inductance which has an inevitable loss of efficiency due to the DCR of the inductor. Efficiency is also increased in the amp supplying the highs as there is no series resistance involved (Usually used in passive xovers to decrease the level of the tweeter to that of the woofer).

As has been indicated above by other posters, any active setup has to be well designed from the beginning. I strongly suggest you learn something about speaker design before attempting anything of this nature. There's no point throwing money at something in hopes of improving it if you don't understand how things work - this is a waste of time and money and is why so many charlatans exist in this industry.

So what's the answer?

YES, it IS possible to increase the quality of sound in this fashion. Any improvements will come in the highs mainly - note that you can use a lower powered amp on the highs in this case. Will you HEAR any difference? Try it and see. (Yes, I wussed out).

Are you claiming that the HPF and LPF sections of the crossover share the same input, even after the external straps have been removed? In my experience this has not been the case. However, I feel that biamping with passive crossovers is not beneficial when compared to a single large amp, assuming the same amps for biamping!. Hooking up two completely different amps will obviously result in a different sound (gain stages are probably mismatched, etc.). I agree with Chu that hooking up two of the same amps in a passive bi-amp config will result in the same sound as using each amp in a monoblock conifg (i.e. using a more powerful amp).

IMO, Active crossovers are only beneficial if the speaker was designed with that in mind (and includes the active crossover). For example, Paradigm's Active 40s (custom amps and active crossovers) was a clear step above their studio line...

Thanks for clarifying Jonathan, you seem to really know what you're talking about. I think that because of the intermodulation distortion in the amplifiers (Chu rolls his eyes ), bi-amping can help (cleaned up highs for me, except I didn't have a good enough bass amp so I had to go back). Also, it can give more headroom to bi-amp than to simply use an amplifier of twice the power rating... the sum of the wave amplitudes with momentary peaks can be double what it was before, that's in theory up to 3db more headroom than a double-power amp with 40% higher voltage rails.

And yes, mirroring a passive network's response is really hard. I'll be trying, soon, to get it "close enough" actively with my speakers. Steep filters and nice linear/accurate drivers help, except mine are iffy.